The present invention relates to a work holding device used in an external form cutting machine for printed boards.
In an external form cutting process for printed boards, several boards having larger sizes (hereinafter, referred to as a blank board) are piled on each other and together fixed to a base plate, which is provided for protecting a working table, by means of pins, and are together cut into boards each having a precise external form (hereinafter, referred to as printed board). This process is for improving fabrication efficiency. In prior arts such as disclosed in Japanese Utility Model Laid-open No. 61-5509, the cutter is surrounded by an annular brush for sucking and exhausting chips produced in cutting. Further, in the final cutting process where the printed boards are completely separated, the brush and an annular rubber member arranged around the brush are operated for pressing both boards in order to prevent the printed boards from shifting relative to the blank boards. However, in the prior arts, when the cutter starts running at a corner of the printed board for fabrication easiness, less than 25% of the brush or the rubber member 2 presses the printed board 1, as shown in FIG. 4. In consequence, when the printed boards 1 are of a large size, the pressing force to the printed boards 1 is not sufficient, causing the printed boards 1 to deviate from their precise positions and to have external forms different from their precise ones. Although an increased pressing force may be obtained by increasing the size of the rubber member, the rubber member of a large size will deteriorate the operational efficiency of the machine. For solving this problem, in the machine shown in FIG. 4, pins 5 are provided, in addition to the pins for clamping the blank boards 3 on the base plate 4, for fixing the printed board 1 to the base plate 4 and for preventing the printed board 1 from shifting in cutting process. However, the pins 5 are required only in the cutting process, and must be removed from the printed board 1 when the printed board is going to be used.